There has recently been proposed a magnetic recording disc cartridge which comprises a hard-type cartridge case composed of a vertically separable pair of sections which are usually connected with each other by ultrasonic welding and a magnetic recording disc, which is a so called floppy disc, contained in the cartridge case. The magnetic recording disc is formed by a magnetic recording sheet and a hub assembly composed of a pair of upper and lower hub members for holding the magnetic sheet therebetween at the peripheral portion of a central hole defined therein. The magnetic recording disc cartridge is mounted in a magnetic recording/reproducing apparatus so that the hub assembly is engaged with a drive shaft of the recording/reproducing apparatus to rotatingly drive the magnetic recording disc with an opening for receiving a magnetic recording head of a recording/reproducing apparatus opened. Opening and closing of the opening are controlled by a shutter member which is rotatingly operated from the outside by a flexible slider means. The cartridge case further includes a transparent hole in the vicinity of the peripheral walls thereof for transmitting optical signals for detecting prevention of recording.
In such a proposed magnetic recording disc cartridge, the hub assembly generally comprises an upper hub member and a lower hub member which are inseparably connected with each other with the peripheral portion of the central hole of the magnetic recording sheet interposed and clamped between the pair of hub members. Under such a state, deformation caused by the clamping force in the interposed portion of the magnetic recording sheet tends to extend outwardly in the outer peripheral direction of the magnetic recording sheet in addition to the central hole. However, according to the proposed magnetic recording disc cartridge, the peripheral portion of the central hole of the magnetic recording sheet is clamped by the entire opposite surfaces of the hub members up to the outer peripheries of the hub members, the magnetic recording sheet is largely deformed over the outer peripheries of the hub members, leading to difficulty in securing eveness of the magnetic recording sheet.
In connecting the top section and the bottom section of the cartridge case by ultrasonic welding means, relative deviation thereof should be strictly prevented to improve the mechanical strength of the portion around the opening for receiving the magnetic recording head so that the magnetic recording disc cartridge may accurately be mounted in the recording/reproducing apparatus.
With respect to the shutter member which is rotatably mounted in the cartridge case, there is provided a return spring between a projection formed in a slider for rotatingly moving the shutter member between an opened position and a closed position and a spring contact pin formed in the cartridge case rearward of the projection. When, in such construction, the shutter member is rotatingly moved to the open position, the spring contact portion of the projection of the slider is subjected to a large spring returning force while the projection is exposedly provided in the outer portion of the cartridge case for operation from the exterior of the cartridge case, leading to disengagement of the projection of the slider from an arcuate guide groove therefor and detachment of the spring from a recessed engaging portion formed in the projection of the slider, thereby causing complicated assembling operation of the slider and difficulty in appropriate operation.
Besides, in rotating the shutter member toward the closing position, the slider is elastically deformed in an arcuate form between the open position and the closed position of the shutter member and tends to be outwardly sprung during sliding movement therebetween. Particularly when the forward end portion of the slider is formed thin to facilitate bending thereof, even slight vibration may cause the deformed portion of the slider to be disengaged from the sliding groove thereof, with the forward end portion of the slider striking a stopper wall of the shutter member in the closed position to disable the closing operation of the shutter member.
In the proposed magnetic recording disc cartridge, further, there is provided a means for preventing erroneous erasing of recorded information by opening and closing the transparent hole for transmitting the optical signal for detecting prevention of recording. The erroneous erasing prevention means comprises a movable member formed by a thin plate having a one-armed resilient member, which is arranged in a sliding portion formed in the cartridge case. The movable member is provided in its upper surface with a projection which is operated through a slot formed in the upper wall surface of the cartridge case, though, if the upper portion of the said projection is placed below the upper wall surface of the cartridge case, it is difficult to manually operate the same from outside the cartridge case. On the other hand, if the projection extends over the upper wall surface of the cartridge case, it may cause erroneous operation by unexpected contact by the operator, to reduce reliability of the erroneous erasing prevention member.